As is known, devices for the separation of a liquid from a fluid flow loaded with liquid droplets have utilized separator structures through which the fluid flow passes in counterflow to the separated liquid. These separator structures form at least two stages and each separator structure has an inlet area for the entry of the fluid flow which is arranged lower than a corresponding outlet area. Typically, the separated liquid flows away on surfaces of the separator structures. Generally, the fluid is a gas or a liquid that has a density which is smaller than that of the liquid to be separated.
In the oil and gas industry, in the treatment of two phase or multi-phase mixtures which contain a discrete phase in the form of aqueous droplets in a gaseous phase, a separation of the phases is often necessary. In the separators used for this, separating methods can be carried out using the force of gravity and/or inertial force in the form of centrifugal forces. In both methods, the flow of gas loaded with droplets of liquid, i.e. the fluid flow, is conveyed to a separating surface on which, on the one hand, a separation occurs by simple deflection of the flow or, on the other hand, by the induction of a swirling flow.
Essentially there are two factors influencing the efficiency of the separators. On the one hand, the droplet size has an influence: the smaller the droplets in the two-phase flow are, the more difficult it is to transport them out of the fluid flow to the separating surfaces. That is to say, only with large droplets is there sufficient inertia to cause a deflection. The second fundamental influence on the efficacy is the re-separation of drops from a fluid film located on the separating surfaces due to a high speed of the fluid flow. The thickness of the liquid film located on the surface of the separator structure influences, on the one hand, the free through flow area which is available. On the other hand, the stability of the film is reduced with increasing thickness: a formation of waves on the fluid film can lead to a droplet being separated.
An increase of the amount of liquid, i.e. of the fluid flow, leads to flooding of the separator and, thus, to the capacity limit of the separator being reached. The efficiency of the separation process decreases drastically in the region of the capacity limit.
A separator structure is known from U.S. Pat. No. 4,744,806 wherein droplets of liquid can be separated from a fluid flow, in particular, a mist from a mist-containing gas stream. This separator structure has a heterogeneous construction transverse to the direction of flow. In main zones with a higher density of the separator structure, liquid is predominantly separated, while in auxiliary zones with lower density, which are arranged between the main zones, separated liquid and liquid entering these auxiliary zones flows away in counterflow to the fluid flow. The drainage by means of auxiliary zones facilitates a reduction of the film thickness in the main zones, thereby increasing its capacity.
It is an object of the invention to reduce the film thickness of a fluid flow on a separating surface in a separator in order to increase the capacity of the separator It is another object of the invention to provide an apparatus in which liquid can be efficiently separated from a fluid flow loaded with liquid droplets.